1. Field of the Invention
The present invention relates to a disc array unit, and more particularly, to a disc array unit management system which can improve availability and scalability of the disc array unit.
2. Description of the Related Art
In recent years, an increasing number of organizations are building their storage network by connecting multiple servers around a large-capacity disc array unit, with the view to ensure various advantages, including more efficient use of capacity, more highly integrated management, and faster backup performance.
For organizations operating such a system, the reliability, availability and scalability of the disc array unit are of critical importance. A typical disc array unit has dual components in order to prevent a single failure from causing the entire unit to go down, and is designed to be highly scalable by allowing for the addition of discs, cache memories and controllers with ease without interrupting the operation of the entire unit. Examples of such a disc array unit include the units disclosed in Japanese Patent Laying-Open (Kokai) No. 2003-15826 Official Gazette (Literature 1) and Japanese Patent Laying-Open (Kokai) No. Heisei 11-224164 Official Gazette (Literature 2).
In addition, it is becoming common for a disc array unit to support various storage solutions for higher functionality. These solutions are typically implemented in the disc array unit as software to provide a range of additional functions, such as data backup, creation of duplicate volumes, performance optimization, virtualization and load distribution. Once these additional functions are incorporated, the disc array unit can perform data backup and various other functions as listed above by interoperating with storage management servers or operations servers.
In order to implement these solutions (additional functions), a wide variety of management information must be held in the shared memory of the disc array unit. Since a typical disc array unit is inherently provided with a large-capacity cache memory, there are no difficulties in sparing only a small portion of the cache memory for use as an area for management information.
However, solutions to be incorporated in a disc array unit are becoming wider in variety, sometimes causing a problem of requiring a considerable portion of its memory capacity to be used as a management area for these solutions. This problem can be addressed by use of hardware, which has recently experienced a considerable improvement in scalability. A user can implement a cache memory that can meet the current capacity requirement and extend the memory capacity as necessary anytime in the future. Along with this trend toward a highly flexible extension of memory capacity, it is becoming increasingly important also to achieve scalability in terms of adding solutions, so that a solution can be implemented (incorporated) as it becomes necessary.
Some solutions require a large memory capacity for storage of management information. Therefore, it is desirable that implementation of an additional memory for management information is not necessary when the user does not have such a solution incorporated, but once the user decides to incorporate such a solution, the user can add the solution (function) dynamically without needing to stop the unit even while it is operating.
As described above, scalability in terms of adding solutions is becoming increasingly important, and it is thus desirable that (a) if the user does not need to use a solution that requires a large-capacity memory for management information, the user does not have to implement an additional memory for storage of management information; and (b) if the user should need such a solution in the future, the user can add the solution (function) dynamically without needing to stop the unit even while it is operating. Many of conventional disc array units deal with such over-time changes in user needs by initially securing ample memory area for storage of management information on the assumption that the user may incorporate and use a variety of solutions in the future. This means that a user who needs few or no solutions must tolerate inefficiency that arises from having an additional wasteful memory that will never be used. Furthermore, a conventional disc array unit typically requires the memory map to be updated whenever a solution is incorporated, making it extremely difficult for the user to extend the existing functions dynamically without stopping the operation of the disc array unit itself.
Some manufacturers expect users to add a shared memory when they add solutions (additional functions) or extend an existing cache memory size to a larger one. However, most manufacturers have conventionally secured more than adequate memory area for storage of management information in anticipation of a future increase in memory capacity through the addition of a memory. In this case, if a memory is not added as anticipated, the redundant memory area initially secured will be wasteful, leading to unnecessary loss in memory efficiency.